It is known in the field of electromechanical transducers that a time changing magnetic field near an electrical conductor induces a voltage across the conductor and a current to flow if there is a closed loop current path. The reverse is also true: a time changing current through an electrical conductor will cause a time changing magnetic field. This is the principle under which electromechanical transducers, which includes linear alternators and motors, function.
A prior art electromechanical transducer, specifically an alternator, is shown in U.S. Pat. No. 4,602,174 to Redlich. In order to increase the magnetic flux passing through the electrical conductor (to thereby increase the current generated), a coil of wire is used and a magnet reciprocates in a central passage near the center of the coil. A further enhancement is the formation of a relatively high permeability material into a flux loop through the coil. A magnet reciprocates, not inside the coil, but in a gap formed between flux path structures, and the magnetic flux flows through the structure inducing a current in the coil.
The magnets which are to be reciprocated in the gap are often embedded in a support structure which also passes through the gap. The support structure is a rigid body which permits the structurally weak magnets to be drivingly connected to another body. Since the support structure (which is commonly electrically conductive) also encounters a time changing magnetic field, current is induced in the support structure causing energy losses. These losses reduce efficiency, and the heat generated by this undesirable current can damage the magnets.
The most common configuration for a linear electromechanical transducer is the circular, axisymmetric grouping shown in FIGS. 1A and 1B. A cylindrical magnet support structure 12 reciprocates longitudinally in a gap 14 formed between flux loop segments 10 and 16. Typically, structure 12 is made up of an electrically conductive support into which magnets are embedded. As the support structure 12 reciprocates in the gap, a time varying magnetic flux passes through the support structure 12. Eddy currents are induced in the support structure from the time changing magnetic field which the support structure 12 encounters, causing a net flow of electrical current around the circumference of the support structure 12. The circumferential flow of current causes I R losses since unwanted, unusable current is generated in the support structure 12.
There is a need for a magnet support having negligible losses due to the induced current, while providing a rigid support for the magnet segments.